Method of forming an electrical connection



Au 13, 1957 c. N. HOLTZAPPLE ,8

METHOD OF FORMING AN ELECTRICAL CONNECTION Filed Feb. 1. 1949' 2 Sheets-Sheet 1 INVENTOR CLYDE N HOLTZIPP L E L ATToRN 4 1957 c. N. HOLTZAPPLE vMETHOD 0F FORMING AN ELECTRICAL CONNECTION Filed Feb. 1. 1949 2 Sheets-Sheet 2 I INVENTOR CLYDE N HOLTZAPPLE ToRNEYs,

United States Patent METHOD OF FORMING AN ELECTRICAL CONNECTION Clyde N. Holtzapple, Harrisburg, Pa., assignor to Incorporated Application February 1, 1949, Serial No. 73,946 7 Claims. (Cl. 29-15555) This invention relates to crimped electrical connections and to methods and means for the formation thereof.

In the formation of electrical connections it has been customary to enclose a wire-end in an electrically con ducting metal ferrule to which a terminal lug or some other conducting member is or can be connected, or to enclose a plurality of wire ends in such a ferrule. In the recent past, it has been proven advantageous as shown in the patent of William S. Watts No. 2,410,321, to enclose such a connector-ferrule in a sleeve 01' cylindrical shell of plastic insulating material, whereupon opposite sides of the assembly are pressed laterally toward each other and the metal ferrule is pressed into electrically conducting and mechanically strong connection with the conductor or conductors therein. The areas so compressed have been of various extents and have been in some cases directly opposite each other, e. g., as represented by the tool of the Carlson Patent No. 2,359,083 and in other cases staggered, as shown in the Macy application Serial No. 580,841 filed March 3, 1945, now Patent No. 2,639,754, issued 'May 26, 1953.

Connection assemblies covered with plastic insulation before compression onto electrical conductors and compressed in this fashion have not been completely foolproof, and their use accordingly has been somewhat restricted. I have found that defects which occasionally develop in such pressure-crimped electrical connections, principally the weakening of the insulating sleeve as to dielectric breakdown, are due to localized extrusion or squeezing out of the plastic material of the insulating sleeves during the crimping operation, or to penetration of-the insulation by projections or sharp edges on the ferrule or the crimping tool.

'il-have found further that if there is provided a crimping die with a peripherally confined die cavity having opposed smoothlycurved, pressure-applying surfaces which are largeenough and free from major irregularities and from sharp corners and projections throughout their extent, the tendency of a ferrule to be seriously weakened or punctured'by local extrusion is greatly reduced and can be substantially overcome by the peripheral compression of the ferrule which causes surrounding material to resist such squeezing out around each point under compression. Thus the plastic materials, both metal and insulating plastic, at each point are confined so as to transmit a maximum pressure inward toward the center of: the connection.

I have foundthat if the ferrule is further protected against weakening and especially against cutting into its outer layer reliability of the resulting connection is furtiter-increased, permitting application of greater crimping force without serious impairment of the connection. If the .ends of the die at the longitudinal edges of the diesurfaces recede from the die surfaces so abruptly as substantially to avoid their obliquely pressing against the: material extruded from under the die during crimping',.';weakehing'of the outer material of the ferrule at thatzpointcanlbe substantially avoided.

With the foregoing and other considerations in view, the invention has for an object the provision of a method of making strong, durable, electrical connections of lasting high conductivity, which is adapted to use on insulated connectors and which further can be reliable, simple and economical.

Another object is the provision of a method of forming electrical connections which is simple, expeditious, and effective, and wherein insulation is effectively distributed over the insulated surfaces of the connection.

Another object is the provision of a method of crimping plastic ferrules which can be performed with ease, and which will reduce the distortion of material of the connection due to the crimping operation and in the case of insulated ferrules can obtain a high degree of insulaand the accompanying drawings, wherein I show and describe preferred embodiments of my invention. It is to be understood that these are not intended to be exhaustive nor limiting of the invention but, on the contrary, are given principally for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify and adapt it in various forms, each as may be best suited to the conditions of a particular use.

In the accompanying drawings:

Figure 1 is a view in axial section of an electrical connector of the type having an insulating sleeve permanently secured on its ferrule;

Figure 2 is a sectional view on an axial plane perpendicular to that of Figure 1, of a connection made with the connector as shown in Figure 1 by compression onto an electrical conductor, or wire, in accordance with this invention; I

Figures 3 through 6 show diagrammatically, the successive stages in the compression of a connection assembly, Figure 6 being the final stage shown also in Figure 2, Figures 3 to 6 being on an enlarged scale partly in section taken at the line 66 in Figure 2;

Figure 7 is an isometric representation of a second embodiment of this invention in an electrical connection of the plug type;

Figures 8 through 10 are axially-sectioned views on an axial section corresponding to that of Figure 2 but showing further embodiments of this invention in electrical connections;

Figure 11 is an isometric view of die blocks of the type shown in Figures 2 through 6;

Figures 12 and 13 show two types of hand-operated tools having compression dies similar to those shown in Figure 11; and

Figure 14 is a cross-sectional view of a modified form of die structure embodying this invention.

As exemplified in Figure 2, disposed between crimping dies 37 and 38 there is provided an electrical connection comprising an electrical conductor 20 which in the present instance is in the form of an insulated wire, the end portion of which is exposed as at 22 and the main portion of which carries permanent insulation 24, and an electrical connector of the type shown in Figure 1. The exposed portion of the wire 22 is assembled Within the insulated connector-ferrule 23. Copper, especially soft copper, is well suited as the material for the metal conductive part of such a connector ferrule, since it will yield as a plastic material to pressure transmitted through an outer plastic sleeve 26, but harder metals can be used in connections crimped in accordance with this inven- Patented Aug. 13, 1957 be of a usual type e. g., formed by stamping or rolling to a cylindrical ferrule 25 one end of a sheet metal blank; leaving it integrally attached to a tongue portion 27. If thus made from fiat strips, all sharp edges should be removed, e. g., by tumbling or otherwise polishing. Seamless tubing or drawn seamless sleeves or thimbles are advantageous for this purpose because the drawing process lends itself well to production of a smooth ferrule free from sharp edges and projections. Or, one may use a combination of a ferrule made from fiat stock and a thin seamless drawn sleeve e. g., as set forth in the application of Robert C. Swengel Serial No. 523,004, filed February 19, 1944. The ferrule 25, and in this case the adjacent end of the insulation 24 on the wire, are enclosed in a sleeve 26 of insulating material such, for example, as one of the common insulating plastics, of which vinylite (e g., a copolymer of 97% vinyl chloride with 3%. vinyl. acetate), nylon, and vinylidene chloride polymers (Saran) are examples. The plastic is slightly plasticized (e. g., with known plasticizers) if necessary to give it the property of cold-molding in the dies without fracture. This is further described and claimed in the Patent No. 2,410,321, issued to William S. Watts. Watts shows a plastic ferrule-insulating sleeve extended over the permanent insulation of an electrical conductor and crimped on said permanent insulation with a crimp presenting roughly the shape of a hexagonal prism or the frustrum of a hexagonal pyramid, and the Carlson Patent No. 2,359,083 presents the pair of angular die surfaces adapted to produce the crimp shown in Watts patent.

The present invention is more perfectly adapted to the crimping of a plastic ferrule and especially a composite ferrule having a plastic insulating sleeve tightly embracing a plastic metal ferrule, onto at least one electrical wire or other conductor with suflicient force to flow both the insulating plastic and the metal and give a physically strong electrical connection of lasting high conductivitythis being done without seriously impairing the plastic insulation or seriously weakening its dielectric strength.

The assembly, in a transverse zone 30 of the ferrule 25, advantageously coextensive with the ferrule, is compressed in such a fashion that the ferrule 25 and the wire 22 are compacted into a joint which is approximately elliptical in cross-section and which provides a strong and permanent electrical connection. I have found advantage in forming to elliptical cross sections about 65% as thick as they are wide. Thicknesses can be, however, from /2 to /6 the width for various applications. .As will be seen from Figure 6, the metal of the ferrule is pressed tightly onto the exposed portion of the conductor 22 and the whole metallic assembly is effectively compacted into a more or less solid mass of metal. Compression of the metal components into a solid mass is essential for many purposes, although a lesser degree of plastic deformation, which leaves some voids between the conductors, is satisfactory for some purposes.

With the use of this invention, the ferrule 25 remains strong and unbroken as also does the plastic sleeve 26. Similarly, the insulating material of the sleeve 26 is evenly distributed without any punctures or dangerously thin.

or weakened portions or other actual or potential weakness.

In the formation of electrical connections in accordance with the invention, as shown in Figs. 1-6, the end of wire 20 is thrust into the ferrule 23 with the exposed end of the conductor in the wire barrel 25. So far as the basic aspects of the present invention are concerned, the ferrule 23 may be extended over the insulation on the wire 24 as in Figure 2, and for this, the outer end of the ferrule may even be of enlarged diameter to accept thicker wire insulation 24. Further, the conductor 20 may be any electrically conductive element adapted to be inserted into the ferrule 25.

The compacting. or. crimping of the assembly is. done with die surfaces 35 and 36 which provides opposed smoothly curved surfaces which are confined by side walls 40 during the crimping operation. These surfaces are advantageously cylindrical as shown (i. e., the surface generated by a straight line, known as the generatrix moving along a smooth curve, known as the directrix, while maintained parallel to a given axis) but small deformations or deviations from true cylindrical surfaces are permissible and are not excluded here. The pressure imposed by these surfaces 35 and 36 is transmited through the sleeve 26 to the ferrule 25 to effect initial flattening; and the peripheral compression upon further compression of the closed die cavity compacts the assembly, as shown in Figures 3 through 6, into a substantially perfect electrical connection. The smooth continuity of these die surfaces over the entire cavity not only assures against substantial weakening of the insulation sleeve 26 but assures a proper transmission of pressure through it to the ferrule 25. Because of the especially uniform transmission of pressure to the ferrule, resulting in part from said form of the die surfaces and in part from the dimensional relation of the die cavity to'the connector assembly, the invention permits ferrules-to be made of harder or thinner metal and a wider range of plastics, including somewhat softer plastics, can be used without danger of breakage. Likewise, ferrules with an unsecured butt seam can be effectively compressed without danger of opening at the seam. In referring to smooth continuity, smoothly curved or smooth" contours it is to be understood that it is freedom from pro-- jections and abrupt corners or abrupt changes in curvature and not surface texture which is in question. The surfaces 35 and 36 of the dies 37 and 38 may be smooth and burnished, but there is advantage in a rougher surface, e. g., as produced by acid etching or sand blasting the die faces.

While it is advantageous in certain instances that both side walls 40 be provided by the same die surface as exemplified, a construction wherein one side wall isv on one die and another side wall is on another die, as shown in the Carlson Patent No. 2,359,083, for example, may readily be employed without departing from the invention in its broader aspects.

In accordance with the invention in certain of its more specific aspects, the shape of the die surfaces 35 and 36 is that of a cylindrical surface whose directrix (i. e. the curve presented by a cross section taken laterally) isa smooth curve. The directrix which has been discovered. to be best for purposes of this invention in its most efficient aspects is one which has a radius of curvature. at the center approximately equal to that of the periphery of the plastic sleeve 26 of the connection assembly to be crimped by the surfaces and its radius of curvature increasing toward the ends (i. e., the side portions, of the die face) so that, when the dies are moved together (Figures 3 through 6), they first contact the sleeve 26 with their central arcuate portions fitting the sleeve and applying pressure over a substantial central area of the sleeve. As the initial pressure flattens the connector to elliptical form, it meets and tits smoothly against the concave die faces 35 and 36 over a broadening area. Ordinarily, it is not necessary to have the radius of the.cen-, tral portion of the trough provided by these surfaces exactly fit the sleeve 26, because the initial pressure is relatively low. It is enough that it so closely approximates that of the sleeve as to fit it after initial flattening and before. severe compression. Thus, the contact of the die surfaces with the sleeve is substantially uniform, and the initial pressure of the die surfaces on the sleeve is substantially uniform, so as to substantially avoid concentration of pressure which might damage the sleeve. In the form shown in the drawings, the die surfaces 35 and 63 have arcuate directrices whose radii are an average of. the radii discussed above, a simplification which I have proven to be, satisfactory- Specifically, in an advantageous case the ratio of the width of the die cavity to radius of curvature is 1.7. Other cases generally lie between 1.5 and 1.8. I

The longitudinal dimension or length of the die surfaces 35 and 36 measured from end to end in the direction perpendicular to the plane presented in Figure 3, is advantageously not less than one quarter of an inch in extent, although shorter lengths as small as one-eighth of an inch can be used in special cases, and down to, but not less'than, four times the average radial thickness of the insulating sleeve in the crimped zone. Advantageously also, the length of the die surfaces, and consequently of the crimped zone formed thereby, is not less than the length of the metal ferrule to be crimped. The lateral dimension or width of the die surfaces, that is the horizontal dimension of the area confined by the die surfaces between their walls 40 as shown in Figure 3, is approximately the diameter of the connector assembly prior to crimping, although it will ordinarily be enough greater than this diameter to provide clearance for easy insertion of the connector assembly into the die.

In the operation shown in Figure 2, note that the crimping die surfaces 35 and 36 extend to the rear, or away from the terminaltongue portion 27, beyond the enclosed metal ferrule 25. This is satisfactory, as long as the following requirement of the peripheral edge 28 of the metal ferrule 25 is met.

Both the inner metal ferrule 25 and the compressing die surfaces 35 and 36 may advantageously be slightly rounded at their longitudinally extreme edges 28, and 39, respectively, i. e., to a slight radius, about .005 to .020 inch being considered appropriate for this radius. If either edge 28 of the metal ferrule, such as sometimes is the case with the edge adjacent the tongue portion, is not enclosed between the die surfaces during crimping, such an edge need not be rounded off. However, if very sharp metal edges engage the plastic in the area in which itis compressed, such edges may cause a reduction in the dielectric strength of the plastic sleeve.

While it is ordinarily more convenient to leave the ends of the dies open so that some extrusion of the plastie is permitted, a further improvement, and a still further increase in the range of plastic materials which can be used, results from extending the die (or an end member cooperating with the die) inward over the end of the ferrule 25 and having the insulation sleeve 26 substantially abut this overhanging portion of the die, so that endwise extrusion is confined.

-It should be noticed that the areas of metal which bear on the plastic sleeve with the full pressure of the crimping operation have no chamfered or gradually rounded edges which would press obliquely on the plastic extruded from beneath the dies during crimping. As mentioned previously, I have found that the walls at the unenclosed, or longitudinally extreme edges 39, Figures 2 and 11, of the die surfaces 35 and 36 advantageously recede sharply from these plastic-engaging surfaces to get the best crimping characteristics, and ferrule edges 28 which engage the area of plastic crimped must also recede sharply. These edges should have only the slight radius discussed in the preceding paragraph. Enclosed or side edges 42 of the die surface 36 would best be so perfectly fitted that the crimping surface 36 forms a smooth curve with the side walls 40 and thus with the opposed crimping surface 35. In practice, these edges are not left sharp, but are slightly blunted or rounded to prevent their being easily damaged. There is, however, advantage if the die is made of a high-stiffness, fatigue-resistant metal like berylium bronze, in sharpening these die edges to a feather edge which can flex so as to permit it to pass beyond the point where the die cavity curves inward. This will give some lateral compression and thereby also facilitates removal of the crimped connection from the die.

It is important that the two opposed dies have substantially smooth and continuously curved surfaces as shown,

to prevent puncture and excessive reduction of thickness of the insulation sleeve, by excluding a cavity at the sides, into which insulation material might extrude; such extrusion and local relief of the confined compression of the sleeve would tend to create a greater likelihood of the plastic becoming locally thinned or even punctured. The sharper the side edges 42 of the die surface 36, and the closer the snug fit between the crimping dies 37 and 38, (that is, the closest they create a peripheral confinement) the more closely an optimum crimp is obtained. Practical necessities, such as preventing damage to the, side edges 42 by slightly blunting or rounding them, need not detract from successful embodiment of this invention in crimping dies as long as the optimums discussed in the preceding paragraph are substantially ad-. hered to.

In Figure 7 we have an electrical connection, of the terminal plug type, in which both a hexagonal insulationgripping crimp, shown generally at 44, and the subject crimp (i. e., embodying the present invention) shown generally at 30, are used, each for the purpose to which it is best suited. The hexagonal-section crimp is used to compress the extended plastic sleeve 26 onto the insulation 24 of an electrical conductor 20, and the crimp 30, as shown in detail in Figures 2 through 6, is used to compress the metal ferrule and wire into a joint without damaging the surrounding plastic sleeve. Both of these crimps 30 and 44 can advantageously be applied simultaneously by a single pair of dies, or by adjoining dies operated as a unit.

Figures 8, 9 and 10 show three additional embodiments in which the insulation sleeves 26 substantially enclose the entire areas of the metallic components. These embodiments have the common function of connecting two or more insulated electrical conductors or wires 20 by compressing previously insulated connector ferrules 25 onto the bared or exposed ends 22 of the wires in the manner shown in Figures 3-6, and shown generally here at 30. These are frequently referred to as Butt (Figure 8), Parallel (Figure 9), and End or Acorn (Figure 10) connectors.

In Figure 8 wire ends 22 are brought end-to-end within an elongated metal ferrule 25b previously enclosed in a plastic sleeve 26b as described, and the assembly is crimped at 30 twice, that is, adjacent the exposed or bared portion 22 of each wire 20. The subject crimp shown in Figures 2-6 could be used for compressing a sleeve on wire-insulation, though the hexagonally shaped crimp (Figure 8) has been preferred for such purposes.

The embodiment shown in Figure 9 is quite similar to the butt connection shown in Figure 8. Here, however, the two bared conductors 22 are side by side in the metal ferrule 25c which, of course, may be shorter than the ferrule used in a butt connection, and the assembly 30 crimped with cylindrically-surfaced dies as shown in Figure 3.

The end or Acorn connection shown in Figure 10 is preferred for many applications. Here the wires are laid side by side as in Figure 9. The plastic sleeves 26d on such connections are closed at one end 32 and are usually expanded as at 29, to incorporate the insulation of both wires 24.

Returning to the crimping dies, Figure 11 shows clearly the spatial relationships between the two die surfaces, 35 and 36, the side walls 40, and their supporting structure 38 and 37. The side walls are so spaced that a connection assembly can be inserted between them easily. These side walls 40, of course, may be in any operational relationship with the die surfaces 35 and 36 which enables said side walls to laterally confine the die surfaces and an enclosed connection assembly during the crimping operation. Most advantageously the side walls 40 are integral as shown with one die portion 37 or 38 but one side wall may be integral with each die as in the Carlson patent cited above, or both side walls may be on" athird die member with the concave dies operating in its groove or bore, .or each side wall may be on a separate die member. The surfaces 35 and 36 meet end walls 55 and 56 with the previously discussed slight radius at the edges 39.

In crimping with dies of the form shown in Figure 11, the side edges 42 of the upper die 38 usually leave thin longitudinal lines in the crimped surface, and the side walls 40 leave flat sides in small portions of the otherwise smoothly curved crimped area. I have found that these discrepancies do not materially detract from the generally elliptically-shaped confined crimp.

Pressure-crimping dies constructed in accordance with the invention may be embodied in a wide variety of crimping tools. In Figure 12, the die 37e provides the surface 35a between Walls 40a. The channel formed by the walls 40a receives die surface 36@ which is located on a projection of die 38a which fits snugly between the walls 40e. The die 37a is dependent from a head 46, and the die 38a is carried on a toggle linkage as shown and is slidable within this head to operate the die 38e with parallel action for moving the dies 37a and 38a relatively to each other in order to provide the crimping cycle as shown in Figures 3 through 6. The tool linkage enables this cycle to be performed by means of closing the handles 47 together.

Another form of construction is shown in Figure 13. Here the die 37] is located on a jaw 48, and the die 38 is located on a similar jaw 48 the jaws 48 and 48 being pivoted at 49 on lever arms 47 which are mutually pivoted at 50. A link 51 connects the jaws at pivot points 52 to complete a linking which enables approximately parallel action of the jaws.

A particularly gentle and uniformly distributed pres- I sure may be applied when rubber or other resiliently fluid cushion is provided on the pressure-crimping surfaces. In this manner the sleeve 26 to be crimped is protected, and a softer plastic insulating sleeve can be used, if desired. Particularly effective results are secured when the rubber is concentrated away from the center lines of the recesses. In Figure 14, dies 37g and 38g are lined with rubber 54 which, as will be seen, is thin at its central portion and thicker at its side portions.

I claim:

1. A method of forming an electrical connection which which comprises combining with a malleable metal ferrule a surrounding insulating sleeve of tough rigid type, highly tensile plastic material, inserting at least one electrical conductor within said ferrule, compressing together in a transverse Zone the said sleeve, ferrule and conductor of this assembly by the application of external pressure distributed over opposed smooth wholly convex substantially cylindrical surfaces, while maintaining substantially complete peripheral confinement of said assembly, said compression being continued until the resultant compressed transverse zone is approximately elliptical in cross section and the metal ferrule and the surrounding sleeve are sufficiently reduced in cross sectional area to insure both effective forging together of the electrical conductor and the ferrule into substantially solid elliptoid cross section lit ferrule and conductor assembly, while being compressed,

between the opposed cylindrical surfaces, is laterally closely confined between flat surfaces extending along the sides of the compression path and the compression is halted while narrow portions of said fiat surfaces are left at the ends of the major dimension of the approximately ellipticalcross section.

3. A method as defined in claim 1 wherein the length of the compressed transverse zone is not substantially less than that of the metal ferrule being crimped.

4. A method as definedin claim 1 wherein the outer end edges of the ferrule are provided with abrupt but slightly relieved. corners where they meet the lateral faces.

5. A method as defined in claim 1 wherein the application of the external assembly compressing pressure is eifected first on diametrically opposed longitudinally extended middle areas of the sleeve surface and is gradually extended laterally therefromin both directions and the lateral faces of the assembly are subjected to reaction pressures by containing them between closely confining Walls while said'compression is taking place.

6. A method as defined in claim 1 wherein the compression is continued until the maximum thickness of'the transverse zone is /2 to /6 its maximum width.

7. Amethod as defined in claim 1 wherein the ferrule is peripherally compressed throughout and materials of the sleeve, the ferrule and the conductor are extruded longitudinally from said transverse zone with consequent work hardening in all parts of the resulting connection.

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